Method of manufacturing a switch substrate

ABSTRACT

A switch substrate for a switching device that includes an electrical contact brush, the substrate formed with alternating conductive and insulating portions on its surface and having a groove formed between the conductive and insulating portions to eliminate insulating abrasion powder from the surface of the contact brush. The top of the conducting portions is higher than the bottom of the groove but can be above or below the surface of the insulating portions. To form such a substrate, a conductive layer having projections is formed and is engaged with a mold so that the projections are compressed. After the substrate is removed from the mold, the compressed projections extend to their actual height.

This is a division of application Ser. No. 07/618,032, filed Nov. 26,1990, now U.S. Pat. No. 5,155,306.

BACKGROUND OF THE INVENTION

The invention relates generally to a switch substrate and a method formanufacturing the substrate and more particularly to a switch substratefor a contract type switching mechanism for detecting the rotation andposition of a counter, such as for detecting the position of a characterin a printer.

Several types of switch substrates have been proposed which include asubstrate having alternating conducting and insulating portions and acontact brush that passes over the alternating portions in a contactpath to detect rotation of the substrate. One such conventional switchsubstrate 120 is shown in FIG. 5. Substrate 120 is formed with anelectrically conductive portion 20 having a plurality of electricallyconductive contact positions 25 disposed on a substrate 26 in a contactpath in a clock-like fashion. A plurality of insulating contact portions30 are disposed between contact positions 25. Examples of conventionalswitch substrates include switch substrates in which the electricallyconductive portion is formed of a metal sheet and the insulating portionis formed of insulating synthetic resin. Other conventional switchsubstrates include an electrically conductive portion that is formed ofconductive resin and the insulating portion is formed of insulatingsynthetic resin.

Three embodiments of a conventional switch substrate 61, 62 and 63 areshown in FIGS. 6, 7 and 8, respectively. Throughout the application,similar elements are assigned the same reference numerals. Switchsubstrate 61 is formed with an insulating resin layer 8 disposed on aconductive resin layer 7. An electrical contact portion or conductivepattern 2 of conductive resin layer 7 protrudes through the surface ofinsulating layer 8 and can be contacted by an electrical contact brush4. Switch substrate 62 is similar to substrate 61, except that acontinuity pattern 2' is below the level of insulating contact portion 3of insulating layer 8. A conductive or continuity pattern 2" ofsubstrate 63 is above the level of insulating contact portion 3 ofinsulating layer 8.

The conventional switch substrates have several disadvantages. When theswitch substrate rotates, portions are worn by friction between theswitch substrate and the contact brush. This leads to the accumulationof abrasion powder on the contact brush. The abrasion powder istypically composed mainly of insulating synthetic resin and interfereswith electrical contact between the contact brush and the conductiveportions. This can lead to problems such as chattering.

In FIG. 6, continuity pattern 2 and insulating contact portion 3 are onthe same level. Contact brush 4 is electrically coupled to continuitypattern 2 within the region designated by a double arrow D1 (continuityregion). Conductive pattern 2 has a width of a double arrow E which isas wide as D1. It is desirable to make the width of D1 as small aspossible to detect small displacements and to detect the greatest numberof positions. However, when continuity pattern 2 is formed of conductiveresin, the width of continuity pattern 2 cannot be decreased past apractical limit since there is a minimum size filling limit when resinis molded into a conventional metal mold. When continuity pattern 2 isformed of a metal sheet, there is also a practical minimum size limit informing continuity pattern 2.

FIG. 7 illustrates a switch with a continuity pattern 2' lower than thesurface of insulating contact portion 3. Accordingly, the width ofcontinuity region D2 is shorter than width E of continuity pattern 2'.D2 is narrower than D1. Insulating abrasion powder tends to becomeaccumulated over continuity pattern 2' in the depression in theinsulation portion 3 thereby leading to continuity failure.

Referring to FIG. 8, continuity pattern 2" protrudes above insulatingcontact portion 3. This assists in eliminating insulating abrasionpowder from contact brush 4 to decrease continuity failure. However,raised pattern 2" causes the width or a continuity region D3 to increaseto a width wider than width E of raised continuity pattern 2". Itthereby becomes difficult to detect microdisplacements and to detect aplurality of positions.

Conventional switch substrate manufacturing methods also have drawbacks.An electrical continuity portion is formed and positioned in a metallicmold. The insulating portion of the substrate is then molded thereon. Agap tends to occur between the protruding continuity pattern and themetallic mold when the dimensional accuracy and the positioning accuracyare not sufficiently precise. For that reason, the surface of thecontinuity pattern can become covered by insulating resin. This leads toproduct defects.

Accordingly, it is desirable to develop an improved switch substrate andmethod of manufacture which avoids the shortcomings of the prior art.

SUMMARY OF THE INVENTION

Generally speaking, in accordance with the invention, a switch substrateand method of manufacture in which the substrate permits detection ofmicro-displacements by a contact brush which follows a path along thesubstrate and decreases electrical contact failure caused by accumulatedinsulating powder between the substrate and the brush are provided. Thesubstrate is formed with an insulating layer having an electricallyconductive pattern protruding at the surface of the insulating layer. Agroove is formed in the insulating layer surface adjacent to at leastone side of the conductive pattern, preferably before the conductivepattern in the path followed by the brush, so that the pattern protrudesabove the bottom of the groove. The conductive pattern can be below thesurface of the non-grooved portion of the insulating layer. Duringmanufacture, a conductive resin portion having an electrical continuitypattern is engaged with a mold which compresses the continuity pattern.The insulating portions are then filled while the continuity pattern isunder a state of compression. After the substrate is released from themold, the protruding portions increase in height due to its resiliency.

Accordingly, it is an object of the invention to provide an improvedswitch substrate and method of formation.

Another object of the invention is to provide an improved switchsubstrate which eliminates problems caused by insulating abrasionpowder.

A further object of the invention is to provide a switch substratehaving a high number of detectable positions which can lead to detectionof micro-displacements.

Still another object of the invention is to provide an improved methodof forming a switch substrate in which insulating material is notinadvertently formed over the continuity pattern.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification anddrawings.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others, and thearticle possessing the features, properties, and the relation ofelements, which are exemplified in the following detailed disclosure,and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a plan view of a switch substrate constructed in accordancewith the invention;

FIG. 2 is a cross-sectional view of the switch substrate shown in FIG. 1taken along line A--A;

FIG. 3 is a partial cross-sectional view of the switch substrate shownin FIG. 1 taken along line B--B;

FIGS. 4A, 4B and 4C are partial cross-sectional views or the switchsubstrate of FIG. 1 in use, at sequential moments or time;

FIG. 5 is a plan view of a conventional switch substrate;

FIGS. 6, 7 and 8 are partial cross-sectional views of switch substratesconstructed in accordance with the prior art in use;

FIG. 9 is a partial cross-sectional view of a switch substrate of FIG.1, in use;

FIG. 10 is a partial sectional view of a switch substrate constructed inaccordance with another embodiment of the invention;

FIG. 11 is a partial cross-sectional view of a prior art switchsubstrate, in use;

FIG. 12 is a perspective view of a printer including a switch substrateconstructed in accordance with the invention;

FIG. 13 is partial sectional view of a switch substrate constructed inaccordance with a conventional method; and

FIGS. 14A, 14B and 14C are partial cross-sectional views illustratingsteps for forming a switch substrate in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a plan view of a switch substrate 100 constructed inaccordance with the invention. FIG. 2 is a sectional view taken alongline A--A of FIG. 1 and FIG. 3 is a partial sectional view taken alongline B--B of FIG. 1. Switch substrate 100 includes an electricallyconductive resin layer 7 disposed on an electrically insulating resinsubstrate 8. An electrically conductive pattern 29 of conductive layer 7is present between exposed insulating contact portions 3 of insulatinglayer 8. Continuity pattern 29 is covered with a metal plating 10.

The surface of continuity pattern 29 and plating 10 is below the surfaceof insulating contact portion 3. A groove 6 is provided at the boundarybetween continuity pattern 29 and insulating contact portion 3 in aregion on which an electrical contact brush passes. The bottom surfaceof groove 6 is below the top of continuity pattern 29.

FIGS. 4A, 4B and 4C are partial sectional views of switch substrate 100,in use. As switch 100 is rotated in the direction of an arrow C,continuity pattern 29 passes by a contact brush 4 which follows acontact path over continuity pattern 29 and insulating contact portions3. A quantity of abrasion powder 5 collects at brush 4. FIG. 4Aillustrates the state in which contact brush 4 has not yet contactedcontinuity pattern 29. FIG. 4B shows that when switch substrate 100rotates further, contact brush 4 causes abrasion powder 5 to drop intogroove 6 and the conductive surface of contact brush 4 is exposed and isfree to come into contact with continuity pattern 29. FIG. 4C shows theposition of the elements after contact brush 4 has separated fromcontinuity pattern 29.

Accordingly, switching is conducted in this manner and the chance ofcontinuity failure caused by abrasion powder 5 is significantlydecreased or eliminated. The cleaning function of groove 6 eliminatesthe necessity of raising continuity pattern 29 above the level ofinsulating contact portion 3 in order to remove abrasive powder.However, the level of pattern 29 can be set at any selected height,either above or below the surface of insulating contact portions so longas groove 6 is present. Lowering the height of continuity pattern 29permits a more narrow continuity section.

FIG. 12 shows a printer mechanism 90 including a switch substrate 130mounted on a frame member 91, constructed in accordance with theinvention. Printer 90 also includes a plurality of electrical contactbrushes 44 for detecting the position and micro-displacement of switchsubstrate 130.

EXAMPLE 1

FIG. 9 is a partial sectional view of a switch substrate 100 constructedin accordance with the invention. The outer radius of curvature of a tipportion 41 of contact brush 4 was 0.4 mm. The width of continuitypattern 29 was 0.56 mm and the surface of continuity pattern 29 was 60μm lower than the surface of insulating contact portion 3. The bottom ofgroove 6 was 0.14 mm lower than the surface of continuity pattern 29 andgroove 6 was 0.271 mm wide. The width of a continuity sectioncorresponding to the positions in which contact brush 4 is electricallycoupled to continuity pattern 29 is represented by a double arrow D4.Width D1 of continuity pattern 2 of substrate 61 of FIG. 6 is equal towidth D4 of FIG. 9. However, the chance of continuity failure caused byabrasion powder and the like are significantly smaller for substrate100.

The width of groove 6 and the relationship between the height of thesurface of continuity pattern 29 and that of insulating contact portion3 are merely exemplary and the desired width of the continuity sectioncan be obtained by adjusting each value. For example width D4 can bedecreased to be narrower than D1 by narrowing groove 6 or by loweringthe surface of continuity pattern 29. Width D4 can be made substantiallynarrower than D3 despite having the same width of continuity pattern.Accordingly, the chances of continuity failure in substrate 100 are fewand microdisplacements that are smaller than in similarly dimensionedconventional switch substrates can be detected.

The width of the groove and the difference of height between the surfaceof the continuity pattern and the surface of the insulating contactportion should preferably come within the following ranges: the grooveshould be more than 1 mm wide; the difference of height between thesurface of the continuity pattern and the surface of the insulatingcontact portion should not be more than 100 μm; and the difference ofheight between the surface of the continuity pattern and the bottom ofthe groove should not be less than 5 μm.

The conductive portion of substrate 100 of Example 1 was formed fromconductive resin having metal plating 10 on continuity pattern 29.However, metal plating is not always necessary. Furthermore, thecontinuity pattern can be formed of metal on an insulating substrate andaccordingly, conductive resin is not necessary.

EXAMPLE 2

FIG. 10 illustrates a switch substrate 70 constructed in accordance withanother embodiment of the invention in which the conductive portion ofsubstrate 70 includes a metal sheet 11 having metal plating 10 thereon.FIG. 11 shows a prior art substrate 80 including metal sheet 11, in use.Groove 6 is provided next to a continuity pattern 23 of substrate 70,which is lower than the surface of insulating contact portion 3. Theswitching process and the width of the continuity portion were the sameas those of Example 1. Accordingly, the chance of continuity failure wassmall and microdisplacements which are smaller than those ofconventional substrates can be detected.

The following drawbacks can occur when conventional manufacturingmethods are employed to form switching substrate 70 in which continuitypattern 23 includes a metal sheet and a groove is provided next tocontinuity pattern 23. After the conductive portion is formed, a formedmetal sheet is set and positioned in a metallic mold for use in formingthe insulating portion of the substrate. To form groove 6, the shape ofthe metallic mold for use in forming the insulating portion iscomplicated because a plurality of cut-out portions must be provideddownward on the metallic mold for use in forming the insulating contactportions. The number of cut-out portions is the same as the number ofcontinuity patterns (conductive contact portions). The cut-out portionsand the protruding portions of the conductive portion of the substratemust be closely aligned so that the insulating resin can be formedproperly.

Gaps can occur between the conductive portion and the mold when thedimensions of the metallic mold are not sufficiently accurate and thesetting of the conductive portion to the metallic mold is not adequate.This leads to failure of engagement between the cut-out portions of themetallic mold and the protruding portions of the continuity pattern.Consequently, insulating resin can cover the surface of the continuityportion as shown in FIG. 10.

FIG. 13 is a partial sectional view of a switch substrate 101 which isformed in a conventional manner as follows. A metallic mold for use informing the insulating portion is unintentionally set to the left withregard to metallic sheet 11. An insulating contact portion 3 is formedat an angle with respect to the surface of a continuity pattern 24 sothat the surface of continuity pattern 24 is unintentionally partiallycovered by a finger 31 of insulating contact portion 3'.

Steps for forming a switching substrate 110 in accordance with theinvention are illustrated in FIGS. 14A, 14B and l4C. FIG. 14Aillustrates electrically conductive synthetic resin member 13 which willform the electrical continuity portion of substrate 110. As shown inFIG. 14B, conductive resin member 13 is fitted to a metallic mold 12 anda second insulating synthetic resin member 14 is filled in metallic mold12 and first synthetic resin layer 13 is being compressed therebetween.Second synthetic resin member 14 forms the insulating portions betweenthe electrical contact portions of first conductive resin layer 13. FIG.14C illustrates completed switch substrate 110.

As illustrated in FIG. 14A, first conductive synthetic resin member 13is formed with a protrusion 131 which will act as a continuity pattern27 for contacting a brush. A broken line F indicates the top position ofprotrusion 131 in a non-compressed state. As illustrated in FIG. 14B,first synthetic resin member 13 is compressed by metallic mold 12 beforeforming second synthetic resin member 14. Metallic mold 12 is formed sothat a projection 121 contacts protrusion 131. The area of moldprojection 121 is larger than that of continuity protrusion 131. Abroken line G indicates the position of the top portion of protrusion131 when compressed. The distance between line F and line G, which isshown by a double arrow H indicates the amount of compression of firstsynthetic resin layer 13.

After insulating resin member 14 is formed, the compression forceapplied by metallic mold 12 is released and protrusion 131 is restoredfrom line G toward line F by the resilience of the resin material. Inaddition to the restoration of the height of protrusion 131, secondsynthetic resin member 14 shrinks so that groove 6 is formed next tocontinuity pattern 27. In this manner switch substrate 110 having groove6 next to continuity pattern 27 is obtained and insulating resin doesnot form on the continuity pattern.

EXAMPLE 3

A difference in height of 10 μm, between the surface of the continuitypattern and the bottom of the groove was obtained under conditions that:the first synthetic resin was 0.9 mm thick polyacetal; the secondsynthetic resin was polybutylene terephthalate and the thickness at thebottom portion of the groove was 0.4 mm; and the compression of thefirst synthetic resin was 30 μm. However, acceptable substrates can alsobe formed in which the difference of height between the surface of thecontinuity pattern and the bottom of the groove are varied by changingthe resin material, the thickness and the degree of compression.

The electrical continuity portion is formed by first synthetic resin 13which is compressed by metallic mold 12 for forming second syntheticresin member 14. Accordingly, when the resin material for secondsynthetic resin member 14 is filled, the surface of a continuity pattern27 is not covered by the insulating resin material which forms theinsulating portion of substrate 110. Further, groove 6 next tocontinuity pattern 27, is automatically formed by the resilience of thecompressed first synthetic resin layer 13 and the shrinkage of secondsynthetic resin member 14. Consequently, it is not necessary to setmetallic mold 12 downward, as in conventional methods, for use informing second synthetic resin member 14 in order to form groove 6.

Metallic mold 12 can be set at first conductive synthetic resin layer 13without the engagement of a cut-out portion and a protrusion so that agap will not be produced between first synthetic resin layer 13 andmetallic mold 12 even if the dimensional accuracy and the settingaccuracy are not exactly precise. Formation defects which are causedwhen the surface of continuity pattern 27 is covered by portions ofsecond synthetic resin 14 are prevented to yield a switch substratewhich can detect a microdisplacement and which can be manufactured withhigh productivity.

When a conductive metal sheet is used, rather than conductive resin, itcannot be restored as efficiently as a synthetic resin when thecompression force is released. Furthermore, a metal sheet isdisadvantageous because the size of the apparatus necessary for formingthe substrate increases becomes large and is heavy when the compressionforce is increased. The metallic mold is also worn at the contactportion with the metal sheet and the lifetime of the metallic mold isshortened.

The configurations of the invention can be applied to a switch substratein which the continuity portion and insulating portion of which arecomposed of synthetic resin. However, the present invention is notlimited to such specific embodiment.

In accordance with another embodiment of the invention, the electricalcontact portion can protrude above the surface of the substrate. To formsuch a substrate, the metallic mold is formed without protrusion 121.The first conductive synthetic resin layer is compressed by a flatsurface and the protruding conductive portion extends above the surfaceof the substrate due to its resiliency.

As described above, a switch substrate prepared in accordance with theinvention is provided with a groove which is adjacent to the continuityportion so that abrasion powder which can cause contact failure does notinterfere with contact point of the contact brush. The continuityportion can then come into electric contact with the contact brush.Positive continuity can be provided and the reliability of the switchmechanism can be improved. Because the surface of the continuity patternis lower than the surface of the insulating portion, the size of thecontinuity section can be shortened compared with a continuity patternof even level and a contact type switch mechanism in whichmicrodisplacement can be detected can be provided while positivecontinuity is obtained. Further, a switch substrate which ischaracterized in that a plurality of positions can be detected by asingle switch substrate can be provided.

When the switch substrate includes a first synthetic resin portionforming an electrical continuity portion and also a second syntheticresin portion forming an insulating portion and the two portions areconstructed and arranged so that when the groove adjacent to theelectrical continuity portion is formed by the two resins, the switchsubstrate has the above-described functional effects and the switchsubstrate can be made by the manufacturing method discussed above sothat the forming apparatus can be made compact and the life of themetallic mold can be made long.

The above-described switch substrate having a groove adjacent to theelectrical continuity portion can be easily manufactured as discussedabove without making the shape of the metallic mold for forming thesecond synthetic resin complicated. Accordingly, the switch substratemanufacturing method includes forming a first synthetic resin portion tobe the electrical continuity portion and forming the mold of the secondinsulating synthetic resin portion, compressing the first syntheticresin portion and forming the second insulating resin portion while thefirst synthetic resin is compressed.

This method eliminates problems associated with conventionalmanufacturing techniques, which lead to production defects in which thesurface of the continuity pattern is covered with the second insulatingsynthetic resin. Furthermore, in accordance with the invention, theadhesion between the first synthetic resin and the metallic mold for usein forming the second synthetic resin has been improved and theinfluence caused by setting inaccuracy and dimensional inaccuracy hasbeen eliminated, so that production defect problems have beeneliminated. Accordingly, the quality and productivity of a switchsubstrate are greatly improved.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above method andin the article set forth without departing from the spirit and scope ofthe invention, it is intended that all matter contained in the abovedescription and shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Particularly it is to be understood that in said claims, ingredients orcompounds recited in the singular are intended to include compatiblemixtures of such ingredients wherever the sense permits.

What is claimed is:
 1. A method of forming a switch substrate having aplurality of spaced conductive regions alternating with insulatingregions having outer surfaces along a contact path for use with anelectrical contact brush following the path, comprising:forming a firstmember of conductive resin material, with a plurality of projectionshaving upper surfaces at ends of the projections; placing the firstmember in a metal mold so that the projections are compressed bypressing the upper surfaces of the projections so that the height of theprojections is shortened; filling a region between the mold and thefirst member with insulating material to form a second insulating memberon the first member with insulating material between the projections andnot on the upper surfaces of the projections; releasing the first andsecond members from the mold and permitting the compressed projectionsto increase in height upon release, the upper surfaces of theprojections remaining free of insulating material, having been incompression contact with the metal mold and forming a groove on at leastone side of the projections along the path with the bottom of the groovebeing below the height of an outer surface of the insulating materialand the upper surface of the projections.
 2. The method of forming aswitch substrate of claim 1, wherein the substrate is constructed ofmaterials and under compression pressure such that a surface of thesecond insulating member defining the bottom of the groove decreases inheight after the substrate is released from the mold.
 3. The method offorming a switch substrate of claim 1, wherein the projections and themetal mold are dimensioned so that the upper surfaces of the projectionshave a height less than the height of the outer surface of theinsulating portions along the path.
 4. The method of forming a switchsubstrate of claim 1, wherein the projections and the metal mold aredimensioned so that the upper surfaces of the projections have a heightgreater than the height of the outer surface of the insulating portionsalong the path.
 5. The method of forming a switch substrate of claim 1,including plating with metal the surface of the projections extendingthrough the insulating member.
 6. The method of forming a switchsubstrate of claim 1, including forming a groove on both sides of theprojections along the path.